Stéphan Zientara

Les encéphalites et encéphalomyélites équines regroupent des affections du système nerveux central ayant des causes diverses, dont certaines présentent des enjeux majeurs de santé animale, de biosécurité ou de santé publique. Leur expression clinique est souvent peu spécifique et peut associer des modifications du comportement ou de l’état de conscience, de l’ataxie, de la faiblesse, des fasciculations musculaires, des tremblements, des déficits des nerfs crâniens, de la dysphagie, une parésie, un décubitus ou des convulsions. Face à un cheval présentant une atteinte nerveuse centrale aiguë, l’objectif initial du praticien n’est donc pas nécessairement d’identifier immédiatement l’agent causal, mais de sécuriser l’animal et les intervenants, localiser l’atteinte nerveuse, recueillir une anamnèse clinique et épidémiologique détaillée et identifier rapidement une éventuelle origine infectieuse nécessitant des mesures sanitaires. En France et en Europe, la myélo-encéphalopathie à herpèsvirus équin de type 1 (EHV-1), l’infection par le virus West Nile [WNV] et, selon le contexte, la rage, figurent parmi les causes infectieuses importantes à exclure. Les méningo-encéphalites bactériennes ou parasitaires et d’autres flaviviroses doivent également être considérées. Les encéphalites équines exotiques (encéphalites équines de l’Est, de l’Ouest et vénézuélienne) ainsi que la myélo-encéphalite équine à protozoaires prennent surtout leur importance chez des chevaux ayant séjourné dans des zones géographiques compatibles. L’expansion récente du WNV en France modifie particulièrement le raisonnement clinique : le risque ne peut plus être considéré comme limité aux régions méditerranéennes historiquement touchées. Parallèlement à son statut de malade, le cheval infecté constitue une sentinelle de la circulation virale locale. La prise en charge d’une atteinte nerveuse centrale aiguë s’inscrit ainsi à l’interface entre neurologie clinique, infectiologie, biosécurité et surveillance « Une seule santé ».

Le virus West Nile (WNV) est un arbovirus transmis principalement par les moustiques du genre Culex et maintenu dans un cycle enzootique impliquant les oiseaux comme hôtes amplificateurs et réservoirs. L’Homme et le cheval sont des hôtes accidentels et terminaux, mais peuvent développer des formes neurologiques graves. Longtemps associée en France au pourtour méditerranéen, la circulation du WNV connaît depuis plusieurs années une intensification et une extension géographique vers l’ouest et le nord du territoire, faisant désormais de cette infection un enjeu sanitaire à l’échelle nationale. Chez le cheval, la majorité des infections restent asymptomatiques, mais les formes cliniques sont dominées par des manifestations neurologiques variées. Toute suspicion doit conduire à une prise en charge vétérinaire rapide, à un diagnostic de laboratoire et au signalement selon les procédures règlementaires en vigueur. En l’absence de traitement antiviral spécifique, la prise en charge est symptomatique et de soutien. La vaccination équine, associée aux mesures visant à réduire l’exposition aux moustiques, constitue un outil essentiel de prévention. Au-delà de sa dimension clinique, le WNV constitue un exemple emblématique de l’approche « Une seule santé ». La détection d’un cas équin témoigne d’une circulation virale locale impliquant simultanément oiseaux, moustiques et environnement, et peut ainsi fournir un signal précoce pertinent pour la santé publique. L’intégration des surveillances humaine, équine, aviaire et entomologique permet de transformer ce signal individuel en information sanitaire territoriale. Dans un contexte d’expansion du WNV en France, le vétérinaire équin occupe donc une position centrale, à la fois dans la détection des cas, la prévention et l’alerte sanitaire. Le cheval apparaît ainsi non seulement comme un patient à protéger, mais également comme une sentinelle de la circulation du WNV au service d’une surveillance « Une seule santé » du territoire.

Orthoflaviviruses are etiological agents of neurological diseases in equines. Horses are susceptible to equine Tick-borne encephalitis virus (TBEV), Usutu virus (USUV), and West Nile virus (WNV), although mostly WNV has been associated with clinical disease. The aim of the present study was to estimate the prevalence of TBEV, USUV and WNV in 289 healthy horses from nine provinces of Algeria. This study was conducted between March 2021 and December 2023. Sera that tested positive, doubtful, or negative close to the doubtful threshold in the Orthoflavivirus-ELISA were further tested by the virus neutralization test (VNT), using TBEV, USUV, and WNV strains. The prevalence of Orthoflaviviruses antibodies by ELISA was 23.18% (67/289) compared with 16.95% (49/289) and 0.69% (2/289) detected by WNV and USUV VNT, respectively. TBEV antibodies were not detected in any samples. WNV seroprevalence varied with age, breed, climatic zones and altitude of the horses’ locations. This is the first screening of horse sera for TBEV in Algeria. This study indicates that WNV and USUV have circulated/are circulating in the horse population in three Algerian climatic zones, unlike TBEV, which does not seem to be present.

Between 2006 and 2010, northwestern Europe experienced its first significant bluetongue virus (BTV) outbreak, driven by the spread of BTV-8, which had major repercussions on the European livestock sector. While BTV-3 was first identified in Europe in Italy in 2017, a new introduction of the virus was reported in 2023, in the Netherlands, and subsequently spread rapidly across the continent. A limited number of BTV-3 outbreaks were notified in Belgium in 2023, leading to the loss of its BTV-free status. In the following year, 2024, the virus spread throughout the country in a short time period. This study describes the impact of BTV-3 circulation in Belgium in 2024, detailing both its geographic spread and the associated increase in mortality, reduced births recorded, and decline in milk production among ruminants. Furthermore, preliminary results on the effectiveness of field vaccination and maternal immunity transfer are presented, as well as critical gaps that hinder the development of a robust, evidence-based management strategy. As the epidemiological situation is expected to become more complex in the future, due to the co-circulation of multiple BTV serotypes and other Culicoides-borne diseases, such as EHDV, effective collaboration and communication among stakeholders and international authorities will be crucial for implementing measures to mitigate the spread of these diseases.

Equine infectious anemia virus (EIAV) is the simplest described lentivirus within the Retroviridae family, related to the human immunodeficiency viruses (HIV-1 and HIV-2). There is an important interplay between host cells and viruses. Viruses need to hijack cellular proteins for their viral cycle completion and some cellular proteins are antiviral agents interfering with viral replication. HIV cellular partners have been extensively studied and described, with a special attention to host proteins able to inhibit specific steps of the viral cycle, called restriction factors. Viruses develop countermeasures against these restriction factors. Here, we aim to describe host cellular protein partners of EIAV viral replication, being proviral or antiviral. A comprehensive vision of the interactions between the virus and specific host’s proteins can help with the discovery of new targets for the design of therapeutics. Studies performed on HIV-1 can provide insights into the functioning of EIAV, as well as differences, as both types of virus research can benefit from each other.

Real-time RT-PCR for the detection of epizootic hemorrhagic disease virus (EHDV) in clinical samples is a fast and sensitive tool for the diagnosis and confirmation of disease. Several real-time RT-PCR methods have been reported over the last 10 years. In this chapter, we describe seven duplex real-time RT-PCR assays to amplify part of genome segment 2 of EHDV to enable serotype identification. The assay includes the detection of an endogenous control gene—beta-actin.

The emergence of EHDV in Europe during the autumn of 2022 reinforces the need for molecular tools (RT-PCR) for rapid detection of animals infected with this virus. Viral genome testing can be performed on whole blood under anticoagulant, spleen, and bloody organ homogenates from ruminants. It can also be performed on cell culture following viral isolation tests. Various so-called classical or end-point RT-PCRs will be described, which permit the amplification of a part of the viral genome (targeting segment 7) allowing the detection of EHDV whatever the serotype (pan-RT-PCR) and also to amplify a portion of the gene coding the viral protein (VP) 2 enabling serotyping. The PCR amplification products are visualized by agarose gel electrophoresis. Sequencing of the type-specific RT-PCR amplification products allows for the serotype of the virus to be determined.

In Cuba, despite a high sero-prevalence of bluetongue virus (BTV), circulating serotypes remain unknown. The aim of this study was to identify circulating BTV serotypes in farms throughout the western region of Cuba. Blood samples were collected from 200 young cattle and sheep between May and July 2022 for virological analyses (PCR, viral isolation and virus neutralization) and genome sequencing. The results confirmed viral circulation, with viro-prevalence of 25% for BTV. The virus was isolated from 18 blood samples and twelve BTV serotypes were identified by sequencing RT-PCR products targeting the segment 2 of the BTV genome (BTV-1, 2, 3, 6, 10, 12, 13, 17, 18, 19, 22 and 24). Finally, the full genome sequences of 17 Cuban BTV isolates were recovered using a Sequence Independent Single Primer Amplification (SISPA) approach combined to MinION Oxford Nanopore sequencing technology. All together, these results highlight the co-circulation of a wide diversity of BTV serotypes in a quite restricted area and emphasize the need for entomological and livestock surveillance, particularly in light of recent changes in the global distribution and nature of BTV infections.

Dourine is a sexually transmitted parasitic disease affecting equids. Its causative agent is referred to as Trypanosoma equiperdum and the prescribed serodiagnosis method is the complement fixation test (CFT). In the context of our European Reference Laboratory mandate for equine diseases (excluding African horse sickness), we organised dourine CFT inter-laboratory proficiency tests (ILPTs) in 2015, 2018 and 2022 to evaluate the performance of the European Union network of National Reference Laboratories (NRLs) for dourine. ILPT panels were composed of horse sera with or without antibodies against Trypanosoma spp. originating from non-infected, immunised or experimentally infected horses. Twenty-two NRLs participated in at least one of the three sessions. In 2015, 2018 and 2022, the percentage of laboratories obtaining 100% of the expected results was 57, 90 and 80, respectively. These dourine CFT ILPTs showed the benefits of standardising the method’s detection limit and underlined the constant need to evaluate NRLs to improve the network’s performance. These results also argue in favour of the need for a representative bio-bank to improve the representativeness of ILPT samples and to allow the adoption of alternative serological methods for international surveillance of dourine.